Over the past two decades, electrospinning has attracted great interest from the academic and industrial scientific communities due to its capability for continuous fabrication of ultrafine fibers having diameters from a few nanometers to a few microns (commonly known as “nanofibers”). Unlike conventional fiber spinning processes, the fabrication of these sub-micron fibers is driven by electrical forces rather than mechanical forces, and often involves in high uniaxial extensional strain rates up to 1000 s−1. These fibers can be produced from a wide range of organic and inorganic materials and typically have extremely high specific surface areas, owing to their nanometer-scale fiber diameters. The structural and functional versatility of these fibers, in addition to the economic viability of the process at the laboratory scale, has allowed their use in a broad range of applications (e.g., membranes and filters, battery materials, sensors, biomaterials, drug delivery). In these applications, the mechanical integrity of the electrospun material determines whether it will hold up under end-use conditions that involve stress and strain. Typical Young's moduli of submicron-diameter electrospun fiber range from about 0.1 GPa to about 7 GPa, which are larger than those of the bulk material but still less than those of many conventional synthetic fibers. Moreover, these nanofibers are unable to withstand tearing or rupture under normal conditions of use (e.g., in apparel). Indeed, fiber durability has remained one of the biggest limitations of electrospun fibers for years that has prevented its use in applications such as chemical and biological protection membranes, coatings for electromagnetic interference (EMI) shielding on equipment and personnel, and ultralight-weight protective gear for soldiers. Use of the ultrafine fibers in high performance applications, such as transparent composites, soft body armor, industrial protective clothing or structural cords and ropes, will benefit from increases in their stiffness, strength, and/or toughness.
Thus, there exists a need for nanofibers with improved mechanical properties, and reliable methods of producing such nanofibers.